Electric motor



E. V- COCHRAN ELECTRIC MOTOR Aug. 15, 1950 Filed May 20, 1949 2 Sheets-Sheet l mm om ZN INVENTOR a EARL V. COQHRAN ATTORNEYS Patentecl Aug. 15, 1950 UNITED STATES PATENT Earl Vernon Cochran, Dayton,

Hansen Manufacturing Ohio, assignorto Company, Princeton,

Ind a corporation of Indiana Application May 20, 1949, Serial No 94,461

3- Claims.

This invention relates to electric motors, and particularly to hysteresis type motors.

In electric motors there is always a certain loss which can be accounted for by the fact that the iron parts of the motor are subjected to varying degrees of magnetism as the motor operates and thus have induced'therein parasitic hysteresis losses that contribute in no way to the operating efficiency of the motor.

In the conventional type of motor such as the induction motor, hysteresis losses are kept low in both stator and rotor by proper Slit design and use of soft iron. In the hysteresis motor, the rotor must necessarily be of highly hysteretic material instead oi soft iron. Therefore, the fluctuation of flux density in the rotor as it passes between slots or poles causes the rotor to be put through minor hysteresis loops which result in power losses in the form of heat.

In hysteresis type motors there is a magnetically retentive rotor which is subjected to the action of a rotating electric-field, and the tendency for the rotor to retain magnetism imparted. theretoby the field causes it to look into tep with th field and; to rotate at synchronous speed.

It has been attempted to reduce the hysteresis losses. in a motor of this type bybridgingbetween the oleswith a ma net c b ge ohat. as. the.

rotor turns relative to the stator it does not encounter such severe changes in field strength.

While this method. forv reducing hysteresis losses in the rotor has met with some, success, it still leaves a good deal to be desired, and, acglyi s. nvention hasas. its. rimar Jf a hi h y pr h s o ismotor. arran nt in w iohthe hysteres s ossesin the. rotor are substantially reduced.

Another object of this invention is to provide an electric motor arrangernent wherein the advantages of magnetically bridging adjacent poles is realized but without theuse of mechanical bridging meansextendingbetween the poles,

A stillfurther objectis the, provision of an electric motor of the hystersis typein whioh substantially all of the flun from the field oftl e motor r ads rou he. rotorenol thususeful working flux, bu n hich, hrsteresislosses. in the rotor are reduced to a minimum.

These and other obiectsandadvanilagos will become more apparent upon reference to the follo ng e pt o tokonin nn ion. with. the accompanyingdrawings, in which;

Figure 1" is a side elevationalview of a, motor n r c ccor g o his nven on;,.

forms of pole configurations for the field; poles Figure 4- is a view showing oneof, the preferred Figure 5 is an exploded perspective view of the motor of Figure 1;

gur s 6, 7, 8 and 9 oview sim a o F ga o 4 but showing different pole arrangements ,1 and u es 10, 1. 1 -2and'1s-a e i wss orr ne rotor arrangements. which have been iound satisfactory.

Referring to the drawings, it will be seen in. motor is of the axial Figures 1 and 5 that the air gap type.

first set of field re o o m r n ally spa ed around the. cente a s f he motor and arrang dso. as to. he co. planar. Each field pole has apart 1,2 extending The field: structure comprises a rearwardly therefrom, and at the rear ends the parts l2 engage notches M in a magnetic-plate I6 and are clamped tightly in position by clamping band I 8,

There ar preferably ndividual o s. 29. on; the parts 12 o n rsizinstho iioldrolesandthese o s will. be seen, ar Di tortion-serially oon,- nected so that alternate of the poles in; ageot DD S te polarity at; anyinstant, of oergizatio Axially spaced. from fieldpoles. 1B. is another set ofv oumfer n ial y spaced field: poles... 2.! cor e pond n in, construction. to fioldr po es It in that they have.pa ts.lt xt ndingitherofrom on which r mounted co s .6; nd whiennarts ar connected by w se of fi ld. poles represented byhe p les In a d poles: re at t a h o h r about the. axis of. the mot preferably an amount eq a tooneehalf the distance between any two adja ent poles; of oneset. I will be eviden that; this provides for stag erin of th polesa ound. thesis sen therebetween.

Rotatably mou ted, 0X he? axisof ti .11? motor is a rotary pa t hay ng-shatter and-adapt d or suppo ting th ma netic rim part .14. which is made of magneti allyetentive material...

In Fig re 2,. which i a developm. nt showin the. rotor rim and thefield poles, it. will-rte. seen that the field poles taken in omb nation'proe e a ubs a ia y; G HHHH U w QkL ing; with neehal disposed on one de. of therotor, and the other ha1f di spose.d: on the 0thersida= In poles indicated at H], and which the magnetic: plate. 28- T 22 are o ronmferentially shiftedseries with a phase shifting reactance such as the;

condenser 36. The winding represented by coils 26 is also connected between power lines LI and L2 with the individual coils thereof in series with each other but with no phase shifting reactance.

Figures 2 and 3 bring out the physical relationship of the poles and show how they are shifted relative to each other so that the poles of one set are substantially midway between the poles of M the other set. The arrangement shown in Figure 3 will result in an effective field rotation in the direction of the arrow on Figure 3. As is well known in the art, this rotating field will drive the rotor between the field poles.

While a number of different pole arrangements are possible according to this invention, the preferred manner of arriving at thesizes'of the poles is illustrated in Figure, 4. In this figure, the poles '38 will be seen to be four in number, and with each thereof extending about degrees around the periphery of the field structure. The space between adjacent of the poles is also about 45 degrees. This may be more [generally stated as follows: There are 2N poles ineach set. Each pole has a peripheral extent indicated as angle A in Figure 4 and wherein angle A is equal to or less The angular distance between adjacent of the poles is indicated at B, .and wherein B is equal to'or greater than It will be understood that the number of poles in each set is the same, and that preferably the sets are angularly displaced one halfof the angular distance between. the center lines of adjacent poles. a

In Figurefi a somewhat different pole arrangement is shown, wherein reference numerals 40 indicate theindividual poles. In the arrangement shown in Figure 6, however, the poles are not discrete andseparate, but are joinedby a thin magnetic bridge, as'indicated at 42.

*In Figure '7', the poles 44' are separate, having no magnetic bridge therebetween, but are of greater circumferential extent than those indicated in Figure 4. The ends of the poles 44 preferably taper off somewhat, as indicated at 46.

Figures 8 and 9 illustrate still other pole arrangements with the'poles 48 in Figure 8 having a circumferential extent considerably greater than that shown in Figure 4, and the poles 50 in Figure 9 being considerably smaller.

It will be understood'that the pole arrangemerits shown in Figures 6 through 9 all effect satisflactory operation of the motor, but that the Figure 4 arrangement is to be preferred.

- It has been mentioned that the rotor includes a magnetic rim part of magnetically retentive material, and a number of the possible forms that this member cantake are shown in Figures 10 through 13. Preferably, the rotor rim is main- 4 tained relatively thin, as in Figure 10, in order to obtain the full benefits from the arrangement of this invention. This is preferable because while the magnetic field of the stator which links the rotor rim remains substantially constant at all times, it does shift from one side to the other of the rotor, and by keeping the rotor rim thin,

,the hysteresis losses that'might be occasioned thereby are kept at a minimum.

One of the advantages of the axial air gap type motor is that it is much easier to form the two sets of field poles and the opposite faces of the rotor so that the}, are exactly parallel. This has a tendency further to reduce the variations in field strength encountered by the rotor and assists in maintaining the hysteresis losses in the motor at a minimum. Furthermore, due to the fact that the rotor runs at relatively low speed, the tolerable lack of concentricity thereof about its axis of rotation is considerably greater than the corresponding tolerance that can be given a radial air gap type rotor. I H

Referring to Figure; the operation of the motor can readily be seen. The field poles 20 are energized substantially degrees ahead of poles 26, and, since the poles themselves are staggered, the field has a tendency to move in the direction of the arrow 52. This movement of the field pulls the rotor with it, and, a short period of time after the motor is energized, the rotorwill be in step With the field and will thereafter operate synchronously. v

It is to be noted that while distributed windings for the fields are shown and are to be preferred, each of the two field structures could be energized by a single coil or an arrangement could be arrived at whereby one coil energizes both field structures. Also, while a condenser 3 has been shownas the phase shifting reactance,

and is to be preferred because substantially a 90 degree phase shift can be attained, shading or lagging coils-an inductive reactance, a two phase supply system or other means could be utilized to obtain the desired phase angle between the magnetomotive forces of the two field structures. I

It will be understood that this invention is susceptible to modification in order to adapt it to different usages and conditions, and, accordingly, it is desired to comprehend such modifications within this inventionas may fall within the scope of the appended claims.

Iclaim: f i

1. In synchronous electric motor; a first group of circumferentially spaced co-planar field poles; a second group of circumferentiallyspaced coplanar field poles axiallyspaced from said first group, a rotor having a magnetically retentive rim part of uniform cross section running in said gap, said groups of poles being circumferentially ofiset from each other so as to be uniformly staggered about said gap, meansadjustably supporting said poles for permitting axial adjustment thereof to vary the gap therebetween, an individual ccilmeans for each pole energizable by alternating current for producing alternating magnetomotive forces between alternate poles of each of said groups, and means for shifting the phase of the magnetomotive forces of one group thereby to produce a rotating magnetic field inv said gap, thev amount of said shifting being substantially equal to the. angular offset of the poles of one group from those of the other group, each said pole having a peripheral extent substantially equal to the spacing between the poles of each group.

2. In an axial air gap type hysteresis motor adapted for synchronous operation; a disk rotor having at least its rim part formed of magneti- Cally retentive material and of uniform cross section, a first group of uniformly circumferentially spaced field poles on one side of said rotor and in a plane parallel thereto, a second group of field poles on the other side of said rotor in a plane parallel thereto and also uniformly circuinferentially spaced, the poles of one group being circumferentially shifted relative to the poles of the other group by substantially onehalf the distance between adjacent poles, individual energizing coils for said poles adapted for producing respectively opposite polarities in adjacent poles of each group, and a phase shifting reactance in circuit with the coils for the poles of one group, the circumferential extent of each pole being substantially equal to its spacing from adjacent poles in the same group.

In an axial air gap type hysteresis motor; a disk rotor having at least its rim part constructed of magnetically retentive material, a first group of circumferentially spaced poles on one side of said rotor in a plane parallel thereto, a second group of circumferentially spaced poles on the other side of said rotor in a plane parallel thereto and circumferentially shifted 30 6 one-half pole space relatively to the poles of the first said group, individual energizing coils for the poles of each group and arranged so that alternate poles of each group are of alternate polarity at any instant of energization, and means for supplying energizing current to said coils so the phase difference between the energization of one group of poles is substantially equal to the amount of circumferential shifting of the one group of poles relative to the other, the peripheral extent of each pole being substantially equal to the peripheral extent of the space between adjacent poles in each group.

EARL VERNON COCI-IRAN.

REFEREBHJES CITED The following references are of record in th file of this patent:

UNITED STATES PATENTS NUlfllbGl Name Date 1,419,749 Murphy June-l3, 1922 1,737,128 Ross Nov. 26, 1929 2,234,420 Traeger Mar. 11, 1941 FOREIGN PATENTS Number Country Date 103,184 Australia Feb. 2, 1938 493,928 Great Britain Jan. 11, 1937 

